Create a cron job for age calculation

I have created a cronjob for age calculation named "cronAge" using command

php artisan make:command cronAge 

Below is my Employee Model:

class Employee extends Model
{
    protected $primaryKey = 'tag_no';    
    public $incrementing = false;

    protected $fillable = [        
        'tag_no',
        'emp_type', 
        'age',            
        'date_of_birth',                   
    ];  
}

I am planning to call the cronjob monthly.

protected function schedule(Schedule $schedule)
    {
       $schedule->command('cronAge')
                 ->monthly();
    }

This is my function: Its not a working code. It only shows the logic for calculating the age.

public function handle()
    {
        $emp= new Employee();
        $today = new Date();
        $birth_day = $emp->date_of_birth;
        if ($today.getFullYear() - $birth_day.getFullYear() == 1) {
            if ($today.getMonth() == $birth_day.getMonth()
               && $today.getDate() == $birth_day.getDate()) {            
                $emp->age = $emp->age+1;
            }
        }
    }

So how to implement my logic in the function. Is the logic rite? And please help me in this. I'm new to this cronjob topic and i donno much.

via Chebli Mohamed